This project will develop swept-wavelength laser light sources at several frequencies in the near infrared (NIR). While applicable to numerous applications, the goal is to use these laser sources as an enabling technology for Diffuse Optical Spectroscopic Imaging (DOSI), a technique which allows noninvasive characterization of human tissue and can monitor and predict chemotherapy response in the treatment of breast cancer. During this Phase II project, the sources will be adapted to three specific wavelength ranges that are useful in detecting molecular states of the three most absorbent NIR tissue absorbers: hemoglobin (785-820 nm), lipid (910-950 nm), and water (950-1000 nm). The three light sources will be integrated into a miniature 3 x 3mm NIR laser module for use in a handheld imaging system. This is an enabling technology that will greatly expand technical capability and clinical applicability of optical imaging, as well as the scientific knowledge that will result fro its incorporation into research studies. The technology for the swept optical sources is based on a vertical cavity surface emitting laser (VCSEL) and a micro-electro-mechanical system (MEMS) that allows for wide tunability. The devices require very low power to operate and the fabrication platform is robust, low cost, and adaptable to many applications. Phase I of this project has already demonstrated a prototype swept laser source capable of 1mW output power and 15nm tuning range. Phase II will improve upon these results to realize 5mW optical power and continuous tunability over 35-50 nm, which are practical requirements for a hand-held DOSI system. The swept NIR source will improve the performance and commercialization potential of a DOSI instrument by allowing 3D subsurface imaging, improving the signal to noise ratio of the image by delivering a much higher photon intensity to the detector, and allowing the miniaturization of the device so that it is compatible with routine clinical use. Furthermore, the unique spectral and performance characteristics of this laser open up a wide range of biomedical and other applications that can benefit from a miniaturized swept-source.